The objective of this research is to continue our investigation of the mechanisms of mutagenesis, genotoxicity and DNA repair of a series of DNA adducts formed by chemicals of relevance to human health. The chemicals to be investigated include organic carbonyl compounds, the human carcinogen vinyl chloride, and inorganic complexes of cis- diamminedichloroplatinum(II), an antitumor drug that has mutagenic and carcinogenic side effects. These chemicals differ widely in structure but share at least one common feature: they form cyclic DNA adducts. To accomplish our goals, we propose to use the tools of chemical synthesis and recombinant DNA technology to construct viral DNA molecules that contain, at specific genome locations, the known DNA adducts formed by these compounds. The resultant site-specifically modified genomes will be introduced into bacterial cells, where the single DNA lesion will be acted upon in a presumably normal way by the cell's replication/repair systems. We shall characterize the amount and type of mutations induced through misreplication or misrepair of the adducted genome. We also shall determine the relative genotoxic potentials of the individual adducts formed by the chemicals under study. With this information, we shall attempt to establish formal rules that relate the structure of the DNA lesion with its biological effects. Finally, we shall attempt to elucidate the biochemical pathway(s) by which cyclic adducts are repaired in mammalian cells, by building upon results obtained during the previous grant period.